POS0389 MUSCULAR EXPRESSION OF CD163 AND MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I AS DIAGNOSTIC MARKERS IN IDIOPATHIC INFLAMMATORY MYOPATHIES
Authors: B. Ghang, B. Yoo, S. J. Nam
Journal: Annals of the Rheumatic Diseases (2022)

Background Various inflammatory markers have been suggested for detecting idiopathic inflammatory myopathies (IIMs); however, their diagnostic utility remains inconclusive. Objectives Muscle tissues from patients diagnosed with IIMs from January 2001 to March 2017 in a tertiary hospital were investigated. Muscular expression of CD3, CD4, CD8, CD20, CD68, CD163, MX1, MHC class I, MHC class II, and HLA-DR in muscle biopsy specimens from patients with IIMs and controls were evaluated using immunohistochemical staining. Classification and regression tree analyses were used to classify patients with IIMs who met the 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies (2017 EULAR/ACR criteria for IIMs) using various staining results as predictor variables. Methods Muscle tissues from patients diagnosed with IIMs from January 2001 to March 2017 in a tertiary hospital were investigated. Muscular expression of CD3, CD4, CD8, CD20, CD68, CD163, MX1, MHC class I, MHC class II, and HLA-DR in muscle biopsy specimens from patients with IIMs and controls were evaluated using immunohistochemical staining. Classification and regression tree analyses were used to classify patients with IIMs who met the 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies (2017 EULAR/ACR criteria for IIMs) using various staining results as predictor variables. Results Among the total 146 patients diagnosed with IIMs by expert neurologist or rheumatologist, 129 patients with IIMs met the 2017 EULAR/ACR criteria for IIMs. Histopathologic features consistent with IIMs using HE staining was observed in 104 of 129 (80.6%) patients who met the 2017 EULAR/ACR criteria for IIMs (dermatomyositis, n = 46/66, 69.7%; polymyositis n = 58/63, 92.1%; sensitivity 80.6%, specificity 100.0%). Muscular expression of CD163 (99.2% vs. 20.8%, p &lt; 0.001) and MHC class I (87.6% vs. 23.1%, p &lt; 0.001) were significantly higher in patients with IIMs who met the 2017 EULAR/ACR criteria for IIMs than in controls. Combined CD163 and MHC class I expression provided the most significant stratification for the control group (sensitivity 96.1%, specificity 94.5%). This combination was able to classify 16 of 17 (94.1%) patients who were diagnosed with IIMs by an expert physician but did not meet the 2017 EUALR/ACR criteria for IIMs. Conclusion Combined CD163 and MHC class I muscular expression may be useful in diagnosing IIMs. Table 1. Sensitivity, specificity, and predictive values of various inflammatory marker expressions and their optimal combinations for the diagnosis of idiopathic inflammatory myopathies. Sensitivity Specificity PPV NPV Patients who were diagnosed by an expert physician but did not meet the 2017 EULAR/ACR classification criteria for IIMs are classified by each combination Muscle biopsy features consistent with IIMs on H/E staining 80.6% 100.0% 100.0% 74.5% 7/17 (41.2%) CD3 expression 91.5% 51.4% 77.6% 76.6% 7/17 (41.2%) CD163 expression 99.2% 79.2% 89.5% 98.3% 16/17 (94.1%) MHC class I on myofibers 87.6% 76.9% 88.3% 75.8% 12/17 (70.6%) HLA-DR on myofibers 69.8% 81.5% 88.2% 57.6% 8/17 (47.1%) MHC class II on myofibers 13.2% 72.3% 45.6% 29.6% 6/17 (35.3%) Combination of CD163 pattern and MHC class I on myofibers 96.1% 94.5% 96.9% 93.2% 16/17 (94.1%) Combination of histopathologic examination using HE staining, CD163 pattern, and MHC class I on myofibers 97.7% 94.5% 95.8% 96.5% 16/17 (94.1%) Acknowledgements This work was supported by a research grant from the Jeju National University Hospital Disclosure of Interests None declared